Source: Release Notes for Internet Explorer 7 Beta 2 Preview (lots more interesting IE 7 stuff onhere too)
Uninstalling Internet Explorer 7 Beta 2 Preview
To uninstall Internet Explorer 7 Beta 2 Preview and return to Internet Explorer 6 on Windows XP
Click “Start,” and then click “Control Panel.”
Click “Add or Remove Programs.”
Check “Show Updates” at the top of the dialog box.
Scroll down the list to “Windows XP – Software Updates,” select “Internet Explorer 7 Beta 2Preview,” and then click "Change/Remove."
If "Internet Explorer 7 Beta 2 Preview" does not exist, run %windir%\$NtUninstallie7bet2p$\spuninst\spuninst.exe. You need to have "view hidden folders" enabled.
Edit: you're welcome
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